$log10 (aggregation)
Definition
New in version 3.2.
Calculates the log base 10 of a number and returns the result as adouble.
$log10
has the following syntax:
- { $log10: <number> }
The <number>
expression can be any valid expression as long as it resolves to a non-negativenumber. For more information on expressions, seeExpressions.
$log10
is equivalent to $log: [ <number>, 10 ]
expression.
Behavior
If the argument resolves to a value of null
or refers to a field that ismissing, $log10
returns null
. If the argument resolves toNaN
, $log10
returns NaN
.
Example | Results |
---|---|
{ $log10: 1 } | 0 |
{ $log10: 10 } | 1 |
{ $log10: 100 } | 2 |
{ $log10: 1000 } | 3 |
Example
A collection samples
contains the following documents:
- { _id: 1, H3O: 0.0025 }
- { _id: 2, H3O: 0.001 }
- { _id: 3, H3O: 0.02 }
The following example calculates the pH value of the samples:
- db.samples.aggregate( [
- { $project: { pH: { $multiply: [ -1, { $log10: "$H3O" } ] } } }
- ] )
The operation returns the following results:
- { "_id" : 1, "pH" : 2.6020599913279625 }
- { "_id" : 2, "pH" : 3 }
- { "_id" : 3, "pH" : 1.6989700043360187 }
See also